fix a bug in updateTrainingSet

In case fillPassedSamples find zero passed negatives and leafFA is achieved, function updateTrainingSet will return false and print misleading information, this PR fix the case.

apps/traincascade/cascadeclassifier.cpp

@@ -309,6 +309,7 @@ bool CvCascadeClassifier::updateTrainingSet( double minimumAcceptanceRatio, doub
     int proNumNeg = cvRound( ( ((double)numNeg) * ((double)posCount) ) / numPos ); // apply only a fraction of negative samples. double is required since overflow is possible
     int negCount = fillPassedSamples( posCount, proNumNeg, false, minimumAcceptanceRatio, negConsumed );
     if ( !negCount )
+        if ( !(negConsumed > 0 && ((double)negCount+1)/(double)negConsumed <= minimumAcceptanceRatio) )
             return false;
 
     curNumSamples = posCount + negCount;